1. Field of the Invention
This invention relates to epoxy resin compositions and resin-sealed type semiconductor devices in which the compositions are used. In more detail, it relates to an epoxy resin composition which when cured has excellent heat cycle resistance, humidity resistance and laser marking characteristics, and to a resin-sealed semiconductor device in which this composition is used.
2. Discussion of Background
Because of their outstanding mechanical characteristics, and excellent electrical characteristics at or near room temperature, epoxy resin compositions have been widely used in recent years, not only for adhesives and coating resins, but also as material for electrical insulation. However, with the level of performance required of electrical insulating material and the like consisting of these epoxy resin compositions rising year by year, it has become difficult to meet this requirement with conventional compositions. A particular problem is that as the temperature of such electrical insulating materials rises, there is a marked drop in their electrical characteristics, and improvement is looked for in this area.
A well-known method of curing epoxy resin is by adding to it a curing catalyst such as a tertiary amine, imidazole, a boron trifluoride monoethylamine complex, a boron trifluoride triethylamine complex, or a boron trifluoride piperidine complex. But a drawback of epoxy resin compositions cured in this way was that their electrical characteristics were not good enough, particularly at high temperatures. Another drawback of such compositions was their high level of moisture absorption, which meant that when used for electrical insulating material and the like they were liable to deteriorate through corrosion.
Earlier, a hermetic sealing technique using metal or ceramic was employed to protect semiconductor elements of integrated circuits (IC's), large-scale integrated circuits (LSI's), transistors, diodes, etc. from the outside atmosphere and from mechanical shock. Recently, however, the economic advantage which resin enjoys over other materials has led to sealing with resin, particularly thermosetting resin, becoming the commonest technique.
Epoxy resin compositions for low pressure moulding, which can be used in the low pressure transfer moulding process (which is suited to mass production) are widely used as the resin for such sealing of semiconductors. However, the conventional resin-sealed semiconductor devices obtained by transfer-moulding an epoxy resin composition consisting of (for example) epoxy resin, novolac type phenol resin curing agent, imidazole curing accelerator, carbon black, etc. had a number of drawbacks. One such drawback was that the resin and the semiconductor device sealed by the resin had different thermal expansion coefficients, and the mechanical stress caused by this difference when the semiconductor device was repeatedly exposed to high or low temperatures could lead to breaking of the bonding wires, or to poor connections, within the sealed device.
A further problem was that when the semiconductor device was used in situations of high temperature and humidity, the moisture in the air permeated the resin sealing the device and penetrated within the seal to the semiconductor element itself, which was liable to cause corrosion of the aluminium wiring within the device, resulting in the deterioration of the latter.
A recent development is the use of `laser marking`, in which the surface of the resin sealing a semiconductor is irradiated briefly with a laser beam, in place of the conventional printing with marking ink. But when this process is applied to the epoxy resin compositions conventionally used for sealing, there is no sharp contrast between the marked and unmarked parts, so that only unclear marking is obtained.